Coated material and the use thereof

ABSTRACT

A coated material comprising a substrate which is coated with a layer of a pyrrolopyrrole of formula I ##STR1## wherein R 1  and R 2  may be 4-pyridyl and X 1  and X 2  are O, said compound of formula I being at least partially in the form of a salt of a strong acid, is suitable for use as an optical recording material and, owing to its electrical conductivity and photoconductivity, as antistatically treated material, as sensor, photoreceptor and solar battery.

The present invention relates to a coated material comprising asubstrate which is coated on at least one side with a pyrrolopyrrolewhich is converted with acid vapours into corresponding salts of theacids. The invention further relates to a process for storing andreading information by irradiating the pyrrolopyrrole layer of saidsubstrate with laser light, to the coated material, to the use ofconductive substrates so coated as photoreceptors, for making solarbatteries and sensors, and to the use of so coated dielectric substratesas antistatically treated materials.

Optical recording substrates and media for storing information are known(q.v. for example "Farbmittel/Polymer-Systeme als Datenspeicher" by G.Kampf et al, in Kunststoffe pp. 1077-1081, Carl Hanser Verlag, Munich1986; or "Erasable laser recording in an organic dye-binder optical diskmedium", by M. C. Gupta et al, in J. Appl. Phys. 60(8), 1986, pp.2932-2937.]. In these publications, information is recorded by treatmentwith light of specific wavelengths and intensity or with other suitableenergy-rich radiation, as with laser light. Absorption of the radiationeffects a local rise in temperature at the irradiated areas, so thatpits or local phase transfers are produced at the surface of therecording substrate and/or media by evaporation, softening or melting,and result in a change of the refractive index, of the absorption or ofthe reflectivity. By means of lasers it is possible to produce holes,bubbles or pits of about 1 to several μm² in size, or to effect a phasetransfer, which information can in turn be read by a laser of lesserintensity utilising the altered reflection or light-scattering behaviourof these holes/bubbles/pits or phase transfer. Suitable recordingmaterials are typically metals, synthetic resins or otherlight-absorbing layers containing, for example, dyes.

It is disclosed in EP-A-401 791 that the change in the absorptionspectrum and/or the change in the photoconductivity of specific organiccompounds after their treatment with an organic solvent can be used withadvantage for storing information. To this end, the surface of theorganic recording layer is treated with an organic solvent in the liquidor gaseous state in accordance with the input of information, forexample by spraying the surface from a nozzle, as typically in anink-jet printer.

Surprisingly, it has now been found that treatment of a thin layer ofpyrrolopyrroles on a substrate with vapours of a strong acid effects apronounced hypsochromic or bathochromic and reversible shift of theabsorption maxima in conjunction with a marked colour change. Such layermaterials are therefore admirably suited for use as optical recordingmaterials for storing and reproducing information by irradiation withlaser light, the acid-treated layer acting as photosensitive layer. Thehypsochromic or bathochromic shift can be reversed in surprisinglysimple manner by the action of heat or simply by washing with water.Such acid-treated layers can also be used for providing dielectricmaterials with an antistatic finish.

It has also surprisingly been found that, in contrast to untreatedmaterials, a layer material treated with acid vapours has a lowerelectrical resistance (improved dark conductivity) and an excellentphotoconductivity which can be further substantially enhanced by dopingwith halogens, conveniently with bromine. The layer materials cantherefore also be used for the making photoreceptors, solar batteriesand sensors.

It is an object of the invention to provide a coated material comprisinga substrate which is coated on at least one side with a thin layer of apyrrolopyrrole of formula I or a mixture of pyrrolopyrroles of formula I##STR2## wherein

R₁ is a phenyl or pyridyl radical of formula ##STR3## which radical issubstituted by a tert-amino group, or a is pyridyl group of formula##STR4##

R₂ is a group ##STR5## or has the same meaning as R₁, and R₃ and R₄ areeach independently of the other C₁ -C₁₈ alkyl, C₅ -C₆ cycloalkyl, C₁-C₁₈ alkyl which is substituted by --OH or --SH, or unsubstitutedphenyl, benzyl or phenylethyl, or phenyl, benzyl or phenylethyl which issubstituted by halogen, C₁ -C₁₂ alkyl, C₁ -C₁₂ alkoxy, cyano or nitro,or, together with the linking nitrogen atom, are a 5- or 6-memberedheterocyclic radical selected from the group consisting of pyrrolidinyl,piperidyl, pyrrolyl, imidazolyl, pyrazolyl, triazolyl, piperazinyl,morpholinyl and thiomorpholinyl,

R₅ to R₈ are each independently of one another hydrogen, halogen, C₁-C₁₂ alkyl, C₁ -C₁₂ alkoxy, C₁ -C₁₂ alkylmercapto or cyano, and X₁ andX₂ are each independently of the other O or S, which compounds offormula I are converted at least partially into salts of strong acids.

Depending on the envisaged end use requirement, suitable substratescomprise a very wide range of materials, including paper, glass, ceramicmaterials, plastics, laminates, metals and metal alloys and metaloxides. Depending on the utility, the substrates may be opaque ortransparent.

The layer of compounds of formula I may have a thickness of 500 to 5000Å, preferably of 500 to 4000 Å, more particularly of 500 to 3000 Å and,most preferably, of 500 to 2000 Å.

The layer of compounds of formula I can be converted partially orcompletely into salts of strong acids, depending on the treatment timeof the layer of compounds of formula I with strong acids. Aqueoussolutions or, preferably acid vapours, can be used for the treatmentwith acid. For the purposes of this invention a brief treatment time inthe order of several seconds will normally suffice, in which casesubstantially only the surface of the layer of compounds of formula Iwill be converted into salts.

It is preferred to treat the layer of compounds of formula I withvapours of a strong acid integrally (i.e. on the entire surface),thereby effecting a bathochromic or hypsochromic shift in the absorptionmaximum. Basically any strong acid which has a sufficiently high vapourpressure at room temperature is suitable for this acid treatment.Exemplary of strong acids are nitric acid, hydrochloric acid,hydrobromic acid, trichloroacetic acid and trifluoroacetic acid. Nitricacid is especially preferred in the practice of this invention. Thecolour change normally occurs after only a brief treatment with acid,typically after the layer has been exposed for about 5 seconds to thevapours of nitric acid.

It is a further object of the invention to provide a process for theproduction of the novel material, which comprises bringing a substrate,at least one surface of which is coated with a pyrrolopyrrole of formulaI, into contact with a strong acid and converting the pyrrolopyrrole offormula I at least partially into a salt of the said acid.

Compounds of formula I are known and can be prepared by known methods.Compounds of formula I, wherein X₁ and X₂ are O, and the preparationthereof, are disclosed in U.S. Pat. No. 4,579,949 and in EP-A 353 184.Compounds of formula I, wherein X₁ and/or X₂ is S, are disclosed in U.S.Pat. No. 4,632,893 or can be prepared by the methods described therein,conveniently by thionation of corresponding diketopyrrolopyrroles (i.e.compounds wherein X₁ and X₂ are O).

If one of the substituents R₅ to R₈ of the compounds of formula I ishalogen, or if groups R₃ and R₄ are substituted by halogen, then halogenwill be understood as meaning iodo, fluoro and, preferably, chloro orbromo.

C₁ -C₁₈ Alkyl groups are typically methyl, ethyl, n-propyl, isopropyl,n-butyl, sec-butyl, tert-butyl, n-pentyl, tert-amyl, n-hexyl,1,1,3,3-tetramethylbutyl, n-heptyl, n-octyl, nonyl, decyl, undecyl,dodecyl, tetradecyl, heptadecyl and octadecyl.

C₁ -C₁₂ Alkoxy groups are typically methoxy, ethoxy, propoxy,isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, tert-amyloxy,n-hexyloxy, n-heptyloxy, n-octyloxy, decyloxy and dodecyloxy.

C₁ -C₁₂ Alkylmercapto groups correspond to the above C₁ -C₁₂ alkoxygroups.

C₅ -C₆ Cycloalkyl groups are typically cyclopentyl and, preferably,cyclohexyl.

R₃ and R₄ as substituted phenyl, benzyl or phenylethyl preferablycontain one of the above cited substituents. Unsubstituted radicals areespecially preferred.

Preferred compounds of formula I are suitably those wherein the groupsR₁ and R₂, X₁ and X₂, R₃ and R₄, R₅ and R₆ and R₇ and R₈ are eachidentical.

Also preferred are compounds wherein R₁ is pyridyl or a group ##STR6##and R₂ is a group ##STR7## or has the meaning of R₁, wherein R₃ and R₄are identical and are C₁ -C₁₂ alkyl, 2-hydroxyethyl, 2-mercaptoethyl,cyclohexyl, benzyl or phenylethyl, or, together with the linkingnitrogen atom, are pyrrolidinyl, piperidyl, morpholinyl orthiomorpholinyl, and R₅ to R₈ are each independently of one anotherhydrogen, chloro, bromo, C₁ -C₄ alkyl, C₁ -C₄ alkoxy or C₁ -C₄alkylmercapto.

Particularly preferred compounds are those wherein R₃ and R₄ areidentical and are C₁ -C₄ alkyl, 2-hydroxyethyl or 2-mercaptoethyl or,together with the linking nitrogen atom, are pyrrolidinyl, piperidyl,morpholinyl or thiomorpholinyl, and R₅ to R₈ are each independently ofone another hydrogen, chloro or bromo.

The most preferred compounds of formula I are those wherein R₁ and R₂are 2-, 3- or, preferably, 4-pyridyl, and X₁ and X₂ are O, or thosewherein R₁ and R₂ are a group ##STR8## R₃ and R₄ are each methyl or,together with the linking nitrogen atom, are pyrrolidinyl, piperidyl ormorpholinyl, and X₁ and X₂ are identical and are O or preferably S.

Very particularly preferred compounds of formula I are1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole,1,4-diketo-3,6-bis(3'-pyridyl)pyrrolo[3,4-c]pyrrole and1,4-dithioketo-3,6-bis(4'-dimethylaminophenyl)pyrrolo[3,4-c]pyrrole.

It is also possible to use mixtures of the pyrrolopyrroles of the abovestructures.

It is yet a further object of the invention to provide a process forstoring information in a novel coated material in which the layer ofcompounds of formula I with salts of strong acids acts as recordinglayer, which process comprises irradiating said recording layer withlaser light according to the input of information and changing theabsorption spectrum of the recording layer such that information iswritten and stored at the irradiated areas.

The inventive process is based on the surprising fact that compounds offormula I in the solid state, conveniently in the form of a thin layeron a substrate, undergo a bathochromic or hypsochromic shift of theabsorption maxima when exposed to acid vapours. The protonation ofcompounds of formula I, wherein R₁ and R₂ are pyridyl, normally effect abathochromic shift, whereas the protonation of compounds wherein R₁ andR₂ are a tert-amino-substituted radical, bring about a hypsochromicshift. The different coloured form so induced has superior lightstability, but can be reconverted to the original form without saltswith strong acids, conveniently by heating, typically at a temperatureof about 150° C., whereupon a hypsochromic or bathochromic change incolour results selectively at the heated areas. The above describedprocess is reversible and can be repeated any number of times. Theprocess can be exemplified as follows by the compound of formula I,wherein R₁ and R₂ are 4-pyridyl and X₁ and X₂ are O: ##STR9##Information is written on the violet form with a laser. The absorbedlight energy is converted into thermal energy so as to causedeprotonation and effect a change in colour at the irradiated areas. Theinformation so written and stored can be read out optically any numberof times or, if desired, deleted by non-selective heating of the entirelayer.

A high storage density can be achieved with the novel process. It isthus entirely possible to produce a dot size ("pixel") smaller than μm².

The layer structure of the inventive recording materials used in therecording process can differ in accordance with the manner in which thesystem functions (transmission or reflection). If the recording systemfunctions according to a change in light transmission, the structure maysuitably comprise: transparent substrate/recording layer/if appropriate,transparent protective layer. The radiation for writing and reading outinformation can be applied either from the substrate side of the systemor from the recording layer or protective layer side, the light detectoralways being on the adjacent side.

If the recording process functions according to a change inreflectivity, then other layered structures are possible for thesubstrate: transparent substrate/recording layer/reflective layer/ifappropriate, protective layer (not necessarily transparent), orsubstrate (not necessarily transparent)/reflective layer/recordinglayer/if appropriate, transparent protective layer. In the former case,the radiation is applied from the substrate side of the system, whereasin the latter case the radiation is applied from the recording layer or,if present, from the protective layer side of the system. In both cases,the light detector is on the same side as the light source. The firstmentioned layer structure is generally preferred.

The pyrrolopyrrole layer for the inventive materials is convenientlyprepared by vapour deposition or sputtering under a high vacuum. Theprocedure comprises vapour depositing or sputtering a pyrrolopyrrole ora mixture of pyrrolopyrroles on to a substrate under a high vacuum,followed by protonation with acid vapour. Two or more differentpyrrolopyrroles can be vapourised on to the substrate simultaneously orstepwise, layer by layer (i.e. multilayer application) using two or morevapourising sources. After vapour deposition, the salts of strong acidsare conveniently produced by treating the layer with acid vapours. Thethickness of the recording layer can vary over a wide range. Preferablythe layer has a thickness of 200 to 3000 Å, more particularly of 500 to1200 Å. Most preferably the layer thickness is about 700 to 1000 Å.

Suitable substrates for the utility as information recording materialare typically glass, polycarbonates, polymethylmethacrylates,polyolefins or epoxy resins. Any metals, including metal plates, filmsor foils of e.g. aluminium, as well as metal-coated plastics sheets andfilms, can also be used.

The light-reflecting layer should be so composed that it reflects asquantitatively as possible the light used for reading out information byscanning. Suitable light-reflective materials include, aluminium, gold,platinum, nickel, silver, rhodium, tin, lead, bismuth and copper.Aluminium and gold are preferred. These materials may be coated on to arecording substrate by vapour deposition or sputtering under a highvacuum. The thickness of the light-reflecting layer shall be such thatit reflects the light required for scanning as completely as possible.Thus the layer preferably has a thickness of 1000 bis 3500 Å, moreparticularly of about 2000 Å. For this purpose, reflectors of highreflectance are advantageous in the appropriate wavelength. Thelight-reflective layer conveniently has an optically smooth levelsurface and said surface is of such a nature that the recording layeradheres firmly to it.

As already stated above, the recording layer and the metallic reflectivelayers can be applied by vapour deposition under vacuum. The material tobe applied is first put into a suitable vessel, which may be equippedwith a resistance heating, and placed into a vacuum chamber. Thesubstrate on to which the material is to be deposited is clamped abovethe vessel with the material to be vapourised. The clamp is constructedsuch that the substrate can be rotated (e.g. at 50 rpm) and heated. Thevacuum chamber is evacuated to about 1.3·10⁻⁵ to 1.3·10⁻⁶ mbar (10⁻⁵ to10⁻⁶ torr), and the heating is adjusted such that the temperature of thematerial to be deposited rises to its vapourising temperature. Thedeposition is continued until the layer applied has the desiredthickness. Depending on the system, first the recording material andthen the reflective layer is applied, or conversely. The application ofa reflective layer can in some cases be dispensed with.

It is particularly preferred to apply the metallic reflective layer bythe sputtering technique on account of the good bonding to thesubstrate. The material to be applied (e.g. aluminum) in the form of aplate is used as a "target" electrode, whereas the substrate is mountedon the counter-electrode. First the vacuum chamber is evacuated to about10⁻⁶ torr and then inert gas, e.g. argon, is introduced until thepressure is about 10⁻³ torr. Between the target electrode and thecounter-electrode a high direct current voltage or radio-frequencyvoltage of several kV is applied, optionally using permanent magnets(magnetron sputtering) so as to produce Ar⁺ plasma. The metal particlessputtered by the Ar⁺ ions of the target electrode are uniformly andfirmly deposited on the substrate. Coating is effected within a few toseveral minutes, depending on the target materials, sputtering techniqueand sputtering conditions. This sputtering technique is described indetail in the technical literature (e.g. W. Kern and L. Vossen, "ThinFilm Processes", Academic Press, 1978).

The thickness of the layer formed by vapour deposition can be monitoredwith the aid of an optical system which measures the reflectivity of thereflective surface coated with the absorption material. It is preferredto monitor the growth of the layer thickness with a quartz resonator.

The recording system may also contain further colorants such asinorganic or organic pigments or, in some cases, inorganic or organicadiabatic layers which are inactive to the acid vapour treatment of thisinvention.

As mentioned above, a protective layer which does not impair therecording and reading out of information can, if expedient, be appliedto the recording layer or light-reflecting layer. This embodiment of theinvention is preferred. Suitable protective layers are typicallyUV-crosslinkable polymers based on polyacrylates such as RENGOLUX® RZ3200/003 and 3203/001 sold by Morton International-Dr. Renger or SD-17®sold by DIC. The protective coating is suitably applied by a spin coaterand crosslinked by UV light. The layer thickness is preferably about5-20 μm, more particularly about 8-10 μm.

As already mentioned, lasers are suitable for writing information on therecording layer, including He-Ne lasers (633 nm), argon lasers (514 nm)or diode lasers based on GaAsAl (780 nm), GaAs (830 nm) and InGaAlP (650nm). The information can be written with a light modulator point bypoint or linearly.

The novel process makes it possible to write/store information and isdistinguished by clear edge definition, a high degree of reliability anda low signal-to-noise ratio. The stored information is easily legibleand the recording system is dimensionally stable, light- andweather-resistant, and is also very resistant to temperature changes andUV rays.

As already mentioned above, the process of this invention effects ashift in the absorption spectrum at the irradiated area or areas of therecording material. The shift in the absorption spectrum and/or thestored information can be read out with a photodetector using alow-energy laser. Suitable photodetectors comprise typically PIN diodes,which make it possible to measure the spectral changes by transmissionor absorption and, in particular, reflection.

Thus after exposure 1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyyroleundergoes a visual colour change from violet to red (shift in theabsorption of c. 580 to c. 540 nm), the corresponding 3'-pyridylderivative undergoes a spectral change of c. 550 nm to c. 535 nm, and1,4-dithioketo-3,6-bis(4'-dimethylaminophenyl)pyrrolo[3,4-c]pyrroleundergoes a spectral change from c. 630 nm to c. 740 nm.

Another object of the invention is the use of the novel substrate asoptical recording material.

A still further object of the invention is the provision of whichmaterial consists of compounds of formula I which are at least partiallysalts of strong acids, which material contains the information in theform of bits of higher or lower absorption than their environment in therecording layer.

Further utilities are also possible by virtue of the electricalconductivity and photoconductivity of the material. The conductivity canbe further substantially enhanced by treating the layer of compounds offormula I containing salts of strong acids with halogens, preferablybromine and iodine.

The pyrrolopyrrole compounds of formula I as defined herein can also beused in the form of salts of strong acids to provide dielectricsubstrates with an antistatic finish, in which case the substrate is adielectric substrate. This utility constitutes a further object of theinvention. For this utility the layer thickness of the pyrrolopyrrolesin the form of salts of strong acids is preferably from 500 to 5000 Å,more particularly from 800 to 4000 Å and, most preferably, from 1000 to3000 Å.

By virtue of its photoconductivity, the novel coated material is alsosuitable for making photoreceptors. For this utility the substrateconsists of an electrically conductive material, typically a metal suchas aluminium, and a charge-carrying layer is present on the layer ofpyrrolopyrroles of formula I in the form of salts of strong acids. Theuse and preparation of such photoreceptors and materials for thecharge-carrying layer are known to the skilled person and described,inter alia, in U.S. Pat. No. 4,632,893. The photoreceptors constitute afurther object of the invention. The layer thickness of thepyrrolopyrroles in the form of salts of strong acids for this utility ispreferably from 500 to 4000 Å, more particularly from 800 to 3000 Å and,most preferably, from 1000 to 2500 Å. Such photoreceptors are used inthe technique of xerography.

The novel coated material is also suitable for making solar cells andsolar batteries. For this utility the substrate consists of atransparent electrical material, conveniently of glass coated withelectrically conductive indium/tin oxide (ITO) or with glass coated withthin metal layers, the coated glass acting as transparent electrode, anda further electrode consisting of an electrical conductor, typicallyaluminium, copper or gold, is present on the layer of pyrrolopyrroles offormula I in the form of salts of strong acids. A Schottky barrier forthe charge carrier separation is provided between the photoconductorlayer and one of the electrodes. Such solar batteries constitute afurther object of the invention. The layer of pyrrolopyrroles of formulaI in the form of salts of strong acids preferably has a thickness of 500to 3000 Å, more particularly from 500 to 2000 Å and, most preferably,from 500 to 1500 Å.

A substrate coated with pyrrolopyrroles of formula I is also suitablefor making sensors. For this utility the substrate is preferably also inthe form of an electrode, conveniently a pair of separate electrodes. Itis, however, especially advantageous to apply to the surface a cathodeand an anode arranged in the form of two interlocking combs and on whichthe layer of pyrrolopyroles of formula I is present. The change inconductivity induced by salt formation before and after contact withacids can be determined by measuring the resistances before and afterthe treatment with acids. The layer of pyrrolopyrroles of formula I isthus the active layer. Such substrates arranged as sensors constituteyet a further object of the invention. The layer of pyrrolopyrroles offormula I has a thickness of 500 to 3000 Å, more particularly from 500to 2000 Å and, most preferably, from 500 to 1500 Å.

The invention is illustrated by the following Examples.

EXAMPLE 1

Aluminium is vapour deposited under a high vacuum on to a glasssubstrate to a layer thickness of c. 2500 Å. Then1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole is vapourised underthe same conditions on to the aluminium layer to a layer thickness of c.1000 Å. The recording plate so obtained is exposed for about 5 secondsto nitric acid vapour, whereupon a bathochromic shift occurs (absorptionmaximum: 540 to 580 nm). Electronic information is written dotwise withan Ar⁺ laser of 514 nm wavelength, and the change in reflectance ismeasured at 600 nm with a microscopic spectrophotometer (Carl Zeiss:UMSP 80). The reflectivity before writing is c. 5% and after writing c.53%.

EXAMPLE 2

Example 1 is repeated, but depositing1,4-diketo-3,6-bis(3'-pyridyl)pyrrolo[3,4-c]pyrrole instead of1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole to a layer thicknessof 700 Å. The reflectivity is measured at 580 nm and is c. 25% beforewriting and c. 61% after writing.

EXAMPLE 3

Example 1 is repeated, but depositing1,4-diketo-3,6-bis(4'-dimethylaminophenyl)pyrrolo[3,4-c]pyrrole insteadof 1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole to a layerthickness of 900 Å. The information is written with a laser diode of 780nm wavelength and the reflectivity is measured at 780 nm with a PINdiode. The reflectivity is c. 6% before writing and c. 52% afterwriting.

EXAMPLE 4

Preparation of a photoreceptor

1,4-Diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole is vapour depositedas charge-generating material under a high vacuum on to an aluminiumsubstrate to a layer thickness of c. 1500 Å, and the layer is thenexposed for 5 seconds to the vapours of concentrated nitric acid. Thecharge-transporting layer is then prepared from a solution ofpolycarbonate and 4-diethylaminobenzaldehyde-1,1-diphenylhydrazone (1:1parts by weight) in CHCl₃ to give a 20 μm thick layer of polycarbonateand 4-diethylaminobenzaldehyde-1,1-diphenylhydrazone (1:1). The chargeand discharge characteristics of the photoreceptor are measured with apaper analyzer supplied by Kawaguchi Denki (model SP-428). The chargeacceptance is -1200 V and the E_(1/2) photosensitivity in the visibleregion is 3 Lux.sec (E_(1/2) : the reciprocal energy necessary todecrease the surface potential to one half of its initial value).

EXAMPLE 5

Preparation of a sensor

A glass substrate on the surface of which a pair of gold electrodesarranged in the form of two interlocking combs is mounted is coatedunder a high vacuum to a layer thickness of 800 Å with1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole. A battery of 6 Vand a resistance of 100 kΩ are connected in series to this sensor. Thereduction in resistivity by treating the sensor with vapours ofconcentrated nitric acid is determined by measuring the voltagedeveloped across the resistance. The voltage changes from 6 μV(untreated) to 600 mV.

EXAMPLE 6

Determination of the antistatic effect1,4-Diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole is vapour depositedunder a high vacuum on to an aluminium substrate to a layer thickness of2000 Å, and the positive and negative charges before and after thetreatment with nitric acid vapours are measured with the paper analyzeraccording to Example 4. Negative potentials of 1000 V and 5 V andpositive potentials of 800 V and 8 V are measured.

What is claimed is:
 1. A coated material comprising a substrate which iscoated on at least one side with a thin layer of a pyrrolopyrrole offormula I or a mixture of pyrrolopyrroles of formula I ##STR10## whereinR₁ is a phenyl or pyridyl radical of formula ##STR11## or is a pyridylgroup of formula ##STR12## R₂ is a group ##STR13## or has the samemeaning as R₁, and R₃ and R₄ are each independently of the other C₁ -C₁₈alkyl, C₅ -C₆ cycloalkyl, C₁ -C₁₈ alkyl which is substituted by --OH or--SH, or unsubtituted phenyl, benzyl or phenylethyl, or phenyl, benzylor phenylethyl which are substituted by halogen, C₁ -C₁₂ alkyl, C₁ -C₁₂alkoxy, cyano or nitro, or, together with the linking nitrogen atom, area 5- or 6-membered heterocyclic radical selected from the groupconsisting of pyrrolidinyl, piperidyl, pyrrolyl, imidazolyl, pyrazolyl,triazolyl, piperazinyl, morpholinyl and thiomorpholinyl,R₅ to R₈ areeach independently of one another hydrogen, halogen, C₁ -C₁₂ alkyl, C₁-C₁₂ alkoxy, C₁ -C₁₂ alkylmercapto or cyano, and X₁ and X₂ are eachindependently of the other O or S, which compound of formula I isconverted at least partially into a salt of a strong acid.
 2. A materialaccording to claim 1, wherein the groups R₁ and R₂ and X₁ and X₂ in thecompounds of formula I are each identical.
 3. A material according toclaim 1, wherein the groups R₃ and R₄, R₅ and R₆ and R₇ and R₈ in thecompounds of formula I are each identical.
 4. A material according toclaim 1, wherein R₁ is pyridyl or a group ##STR14## and R₂ is a group##STR15## or has the meaning of R₁, wherein R₃ and R₄ are identical andare C₁ -C₁₂ alkyl, 2-hydroxyethyl, 2-mercaptoethyl, cyclohexyl, benzylor phenylethyl, or, together with the linking nitrogen atom, arepyrrolidinyl, piperidyl, morpholinyl or thiomorpholinyl, and R₅ to R₈are each independently of one another hydrogen, chloro, bromo, C₁ -C₄alkyl, C₁ -C₄ alkoxy or C₁ -C₄ alkylmercapto.
 5. A material according toclaim 1, wherein R₃ and R₄ are identical and are C₁ -C₄ alkyl,2-hydroxyethyl or 2-mercaptoethyl or, together with the linking nitrogenatom, are pyrrolidinyl, piperidyl, morpholinyl or thiomorpholinyl, andR₅ to R₈ are each independently of one another hydrogen, chloro orbromo.
 6. A material according to claim 1, wherein R₁ and R₂ are 2-, 3-,4-pyridyl, and X₁ and X₂ are O, or wherein R₁ and R₂ are a group##STR16## R₃ and R₄ are each methyl or, together with the linkingnitrogen atom, are pyrrolidinyl, piperidyl or morpholinyl, and X₁ and X₂are identical and are O or S.
 7. A material according to claim 1,wherein the pyrrolopyrrole layer forms at least partially salts withnitric acid, hydrochloric acid, hydrobromic acid, trichloroacetic acidor trifluoroacetic acid.
 8. A material according to claim 1, wherein thelayer of compound of formula I has a thickness of 500 to 5000 Å.
 9. Amaterial according to claim 1, wherein the substrate consists of paper,glass, ceramic materials, plastics, laminates, metals, metal alloys ormetal oxides.
 10. A material according to claim 1, wherein the compoundof formula I is selected from the group consisting of1,4-diketo-3,6-bis(4'-pyridyl)pyrrolo[3,4-c]pyrrole,1,4-diketo-3,6-bis(3'-pyridyl)pyrrolo[3,4-c]pyrrole and1,4-dithioketo-3,6-bis(4'-dimethylaminophenyl)pyrrolo[3,4-c]pyrrole. 11.A material of claim 6 wherein R₁ is 4-pyridyl.
 12. A material of claim 6wherein X₁ and X₂ are S.